Hydro-cyclones are widely used in the metallurgical industry for the separation of particles in a slurry according to their size and/or density. Common on-line measurements used in connection with the operation of hydro-cyclones are the flow rate and density of the slurry being fed to the hydro-cyclone and the inlet pressure of such slurry.
As is well known, the proper operation of a hydrocyclone depends on a suitable rotational motion of slurry inside the cyclone, with a core of air along its axis. This rotational motion is also imparted to the underflow of the cyclone, so that the combined axial and radial velocities of this exiting stream result in a spray of nearly conical shape. When a hydro-cyclone is overloaded, the rotational motion of the slurry in the cyclone is altered such that the radial velocity of the slurry emerging from the cyclone as an underflow stream is small compared with its axial velocity, the air core also is disturbed, and a slender rope-shaped discharge or a blockage results.
The actual shape of the hydro-cyclone underflow stream is approximately conical and has therefore a radius at any suitable position below the underflow outlet itself. This radius varies with changes in the variables associated with its operation.
This characteristic has been used to a very limited extent in the past to control the operation of a hydro-cylone, or at least to shut it down or provide an alarm when the shape of the underflow stream corresponds to undesirable operation.
Thus, for example, there is described in U.S. Pat. No. 4,246,576 to Grieve et al, a monitor which is, in effect, a transition detector, and which provides an output indicating simply whether the underflow is "normal" or "abnormal". In effect this monitor simply acts as a switch indicating either of two conditions of the underflow.
U.S. Pat. No. 3,114,510 to McCarthy and Curtis describes another form of underflow monitor which simply determines whether or not the shape (radius) of the underflow is between two limits corresponding to "underload" and "overload". In other words, this monitor simply detects whether or not the shape of the underflow is anywhere within a desired operating range.
As well as reacting to loading, a hydro-cyclone reacts to different compositions of the feed slurry, and the shape of the underflow stream varies accordingly. It has now been found that a most useful method and means of controlling the operation of a hydro-cyclone or circuit embodying same, can be provided by monitoring the shape of the underflow stream over a continuous desired operating range to provide either a digital or analogue control signal.
It is, accordingly, the object of this invention to provide a method of controlling the operation of a hydro-cyclone, or, alternatively, a circuit of which a hydro-cyclone is a component part, in which the shape, or a variable associated with the shape of the underflow slurry from the hydro-cyclone is employed as a measured control variable.
In this specification the term "control" is intended to include the measurement of variables in the system, such as measurement of particle size, flow rates, and other variables.